572 FRANK R. LILLIE 



spermatozoa of Arbacia and Nereis to the secretion of their own 

 kind of eggs is certainly surprising. 



Another effect of their secretions that should be taken into 

 account in this connection is the stimulating effect on the sperma- 

 tozoa. This is more marked in some animals than in others. 

 Thus the spermatozoa of Nereis are so active in the sea-water 

 alone that but little effect of the egg-secretions can be noted; in 

 the case of Arbacia, although the sperm are quite active in pure 

 sea-water yet the egg-secretions greatly increase their activity 

 for a brief time. In the case of the star-fish, according to Von 

 Dungern's account, the spermatozoa tend to be very inactive in 

 pure sea-water, but are aroused to intense activity by the secre- 

 tions of the ova. 



In different animals, therefore, we may expect to find some 

 difference in the effect' of egg-secretions on the activity of the 

 spermatozoa. But the fact that in such widely separated forms 

 as Arbacia and Nereis secretions of the egg cause strong positive 

 chemotaxis of the spermatozoa inclines one to the view that such 

 a reaction may be very wide spread. In a form in which egg- 

 secretions are both activating and directing in their action, the 

 importance of such secretions in favoring the preliminary steps in 

 fertilization can hardly be doubted. 



The experiments, like Pfeffer's earlier ones, indicate that the 

 factor of specificity is probably subordinate in the purely chemo- 

 tactic response. CO2 and acids are in no sense specific, but they 

 are very effective chemotactic agents with Nereis spermatozoa. 

 But the case of Arbacia serves to indicate that substances of the 

 egg, whether specific or not, are more generally effective than 

 simple chemical substances, for its requires such substances, 

 apparently, in the case of Arbacia to produce a reaction of the 

 spermatozoa comparable in quickness and precision to the reac- 

 tion of Nereis spermatozoa to acid, CO 2, or the secretions of its 

 own eggs. 



We have seen that in some respects the chemotactic behavior 

 of spermatozoa of Nereis and Arbacia is different depending on 

 their relative sensitiveness to CO2 and other agents. The much 

 greater power of resistance of spermatozoa of Chaetopterus and 



